GB/T 2918-2018 English PDF (GBT2918-2018)

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GB/T 2918-2018: Plastics -- Standard atmospheres for conditioning and testing
GB/T 2918-2018
GB
NATIONAL STANDARD OF THE
PEOPLE'S REPUBLIC OF CHINA
ICS 83.080.01
G 31
Replacing GB/T 2918-1998
Plastics - Standard atmospheres for conditioning and testing
(ISO 291:2008, MOD)
ISSUED ON: DECEMBER 28, 2018
IMPLEMENTED ON: NOVEMBER 1, 2019
Issued by: State Administration for Market Regulation;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 5
4 Principle ... 6
5 Standard atmosphere ... 6
6 Standard atmosphere levels ... 7
7 Standard temperature and room temperature ... 7
8 Operation steps ... 8
Appendix A (Normative) Plastics reach moisture equilibrium in a conditioning
atmosphere ... 9
Foreword
This standard was drafted in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 2918-1998 Plastics - Standard atmospheres for
conditioning and testing. Compared with GB/T 2918-1998, the main technical changes
except for editorial modifications are as follows:
-- Chapter 2 "2 Normative References" is added (see Chapter 2);
-- The use conditions of standard atmospheres at all levels such as "23/50 is
applicable to non-tropical regions, and 27/65 is applicable to tropical regions"
and the stipulation that "to obtain comparable data, the standard atmosphere of
23/50 shall be used" are added (see Chapter 5);
-- The calibration frequency is added (see Chapter 6);
-- The method for determining the sample conditioning time when equilibrium
cannot be reached for a long time is modified (see Appendix A).
This standard was redrafted and modified in relation to ISO 291:2008 Plastics -
Standard atmospheres for conditioning and testing.
The technical differences between this standard and ISO 291:2008 and their reasons are
as follows:
-- Regarding normative references, the adjustments with technical differences are
made in this standard to adapt to Chinese technical conditions. The adjustments
are concentrated in Chapter 2 "Normative references". The specific adjustments
are as follows:
 ISO 62 is replaced with GB/T 1034 which is identical to the international
standard;
-- The content of 8.1 NOTE 2 is modified into a paragraph;
-- The content of 8.1 NOTE 3 is modified into a paragraph.
This standard also made the following editorial changes.
-- The informative Appendix B "Background information" of ISO 291:2008 is
deleted;
-- References are deleted.
This standard was proposed by the China Petroleum and Chemical Industry Federation.
Plastics - Standard atmospheres for conditioning and testing
1 Scope
This standard specifies the specifications for conditioning and testing plastics and all
types of specimens under constant environmental conditions.
This standard applies to plastics and all types of specimens.
This standard does not include special environments for certain special tests or materials
or for simulating certain specific climatic conditions.
2 Normative references
The following documents are essential for the application of this document. For any
dated referenced document, only the dated version applies to this document. For any
undated referenced document, the latest version (including all amendments) applies to
this document.
GB/T 1034 Plastics - Determination of water absorption (GB/T 1034-2008, ISO
62:2008, IDT)
3 Terms and definitions
The following terms and definitions apply to this document.
3.1 standard atmosphere
Preferably, a constant environment with specified air temperature and humidity and
limited ranges of atmospheric pressure and air circulation rate. The air contains no
significant added components and the environment is not affected by any significant
added radiation.
NOTE 1: The standard atmosphere enables the sample or specimen to reach and maintain the specified
state.
NOTE 2: The standard atmosphere is equivalent to the average environmental conditions of the
laboratory and can be established in a (environmentally controlled) conditioning cabinet, box or room.
3.2 conditioning atmosphere
A constant environment in which samples or specimens are kept before experiments are
8 Operation steps
8.1 Conditioning
The conditioning time is specified in the relevant materials.
When there is no applicable standard specifying the conditioning time, it shall be
implemented as follows:
a) Unless otherwise specified, for standard atmospheres 23/50 and 27/65, not less
than 88 h;
b) Unless otherwise specified, for room temperature between 18 °C and 28 °C,
not less than 4 h.
NOTE 1: For plastic materials, the time required to reach moisture equilibrium is generally longer than
the time required to reach temperature equilibrium.
If the sample cannot reach moisture equilibrium after conditioning according to a), the
conditioning time is longer than t70 specified in GB/T 1034 (t70 depends on the square
of the thickness), and the time required to reach equilibrium meets the requirements of
Appendix A.
For special tests and plastics or specimens known to reach temperature and humidity
equilibrium quickly or slowly, a shorter or longer conditioning time may be specified
in the corresponding material standard in accordance with the requirements of
Appendix A.
8.2 Experimentation
Unless otherwise specified, the conditioned specimens shall be tested in the same
environment or temperature as that for conditioning. In any case, the test shall be carried
out immediately after the specimens are removed from the conditioning atmosphere.